Taiwanese Patent Publication No. 483368 discloses a wrench 40 and a joint 1 for connecting the wrench 40 with sockets 20. The wrench 40 includes a box end and an open end. The joint 1 includes a hexangular portion 10, a small square insert 11 extending from an end of the hexangular portion 10 and a large square insert 12 extending from an opposite end of the hexangular portion 10. In use, the hexangular portion 10 is inserted in the box end of the wrench 40. The small square insert 11 is inserted in a square hole defined in a small socket 20 or the large square insert 12 in a square hole defined in a large socket 20. The hexangular portion 10 is apt to fall from the box end of the wrench 40 although a ball detent 103 is used to retain the hexangular portion 10 in the box end of the wrench 40. 
The present invention is therefore intended to obviate or at least alleviate the problem encountered in the prior art. 